EVEN AFTER you've left the theater, the show can still go on -- on vinyl, anyway.

Here's a quartet of splendid souvenirs from recent Broadway events worth reliving:

"FOLLIES" IN CONCERT -- (RCA Red Seal H BC2-7128). Every home should have one. Thomas Z. Shepard, who has come to be known as the Broadway cast album producer, decided that "Follies," perhaps Sondheim's finest show, needed to be preserved for posterity the right way. So Shepard staged September's all-star, two-nights-only concert recording at Avery Fisher Hall. Sondheim's lyrics balance and blur irony and sentiment, needling our infatuation with the past, noting its intrusion on the present. His music, sumptuously fleshed out by the New York Philharmonic, is a pastiche that simultaneously celebrates and mourns the Broadway musical.

How to pick standouts from this rich field of performances? Immediate attention-grabbers: Barbara Cook's underlining of the sad self- deception of "In Buddy's Eyes"; Mandy Patinkin's frenetic "Buddy's Blues," in which he does a duet with himself; Carol Burnett's affectingly underplayed survivor's anthem "I'm Still Here"; and Elaine Stritch's bawdy "Broadway Baby."

MA RAINEY'S BLACK BOTTOM -- Manhattan SVB 0 53001). August Wilson's play revealed layers of black experience of racism in America by listening in on legendary "mother of the blues" Ma Rainey and her musicians making music and talking in a white-owned 1927 Chicago recording studio. There are plenty of strong stories and potentially violent conflicts in Wilson's drama, and they're colorfully retold here by the actor/musicians. Especially vivid is the reading by Theresa Merritt as the indomitably dignified Ma Rainey, who exercises her power in the only ways she can. Lloyd Richards has directed this production like a radio play, punctuated by vibrant blues and jazz, and "Ma Rainey" vividly makes the transition from stage to record.

BIG RIVER (MCA 6147) -- Veteran country singer/songwriter Roger Miller has distilled the heart and humor of Mark Twain in his cheery, unassuming songs for this musical based on "The Adventures of Huckleberry Finn." The show took seven Tony Awards, providing a few optimistic notes in 1984, a particularly dire year for the Broadway musical. Miller's songs, recorded in Nashville with real country tang and twang, stand on their own, particularly the moving duet, "Worlds Apart," between Huck and the slave Jim.

THE REAL THING -- (Nonesuch 9 78027- 1-P). Gone, but not forgotten, the performances of Jeremy Irons and Glenn Close survive in this immaculately recorded aural "edition" of quicksilver-tongued Stoppard's playful play about passion. It's an ideal "command performance," missing only the sight of the matinee idols, but you can get a visual fix by gazing at the life-size portraits on the record sleeves.